Optimal trajectories for the aeroassisted flight experiment

This paper deals with the determination of optimal trajectories for the aeroassisted flight experiment (AFE). The intent of this experiment is to simulate a GEO-to-LEO transfer, where GEO denotes a geosynchronous Earth orbit and LEO denotes a low Earth orbit. Specifically, the AFE spacecraft is released from the Space Shuttle and is accelerated by means of a solid rocket motor toward Earth, so as to achieve atmospheric entry conditions identical with those of a spacecraft returning from GEO. During the atmospheric pass, the angle of attack is kept constant, and the angle of bank is controlled in such a way that the following conditions are satisfied: (a) the atmospheric velocity depletion is such that, after exiting, the AFE spacecraft first ascends to a specified apogee and then descends to a specified perigee; and (b) the exit orbital plane is identical with the entry orbital plane. The final maneuver, not analyzed here, includes the rendezvous with and the capture by the Space Shuttle. In this paper, the trajectories of an AFE spacecraft are analyzed in a 3D space, employing the full system of 6 ODEs describing the atmospheric pass. The atmospheric entry conditions are given, and the atmospheric exit conditions are adjusted in such a way that requirements (a) and (b) are met, while simultaneously minimizing the total characteristic velocity, hence the propellant consumption required for orbital transfer. Two possible transfers are considered: indirect ascent (IA) to a 178 NM perigee via a 197 NM apogee; and direct ascent (DA) to a 178 NM apogee. For both transfers, two cases are investigated: (i) the bank angle is continuously variable; and (ii) the trajectory is divided into segments along which the bank angle is constant. For case (ii), the following subcases are studied; 2, 3, 4 and 5 segments; because the time duration of each segment is optimized, the above subcases involve 4, 6, 8 and 10 parameters, respectively. It is shown that the optimal trajectories of cases (i) and (ii) coalesce into a single trajectory: a two-subarc trajectory, with the bank angle constant in each subarc (bang-bang control). Specifically, the bank angle is near 180° in the atmospheric entry phase (positive lift projection phase) and is near 0° in the atmospheric exit phase (negative lift projection phase). It is also shown that, during the atmospheric pass, the peak values of the changes of the orbital inclination and the longitude of the ascending node are nearly zero; hence, the peak value of the wedge angle (angle between the instantaneous orbital plane and the initial orbital plane) is nearly zero. This means that the motion of the spacecraft is nearly planar in an inertial space.     

BTT导弹再入段非线性鲁棒控制

针对BTT导弹再入段的非线性模型以及三通道间的较强耦合,研究了模型不确定情况下的解耦和跟踪控制问题。首先分析了BTT导弹在再入段的非线性模型,然后根据微分几何方法检验该模型是否可进行输入输出解耦,并推导出BTT导弹在再入段的非线性解耦控制律,其后分析了在某种匹配不确定情况下导弹动态系统的具体形式,并将李亚普诺夫方法运用到控制器的设计中,得出鲁棒输出控制跟踪控制律。采用该控制方式对某型BTT导弹的六自由度仿真实验结果表明:该鲁棒控制方法在系统存在不确定性的情况下,可保证系统的稳定性,并实现三通道间的近似解耦,使攻角α,侧滑角β和滚动角γ良好地跟踪期望指令。     

Improving science literacy and education through space life sciences.

The National Space Biomedical Research Institute (NSBRI) encourages open involvement by scientists and the public at large in the Institute's activities. Through its Education and Public Outreach Program, the Institute is supporting national efforts to improve Kindergarten through grade twelve (K-12) and undergraduate education and to communicate knowledge generated by space life science research to lay audiences. Three academic institution Baylor College of Medicine, Morehouse School of Medicine and Texas A&M University are designing, producing, field-testing, and disseminating a comprehensive array of programs and products to achieve this goal. The objectives of the NSBRI Education and Public Outreach program are to: promote systemic change in elementary and secondary science education; attract undergraduate students--especially those from underrepresented groups--to careers in space life sciences, engineering and technology-based fields; increase scientific literacy; and to develop public and private sector partnerships that enhance and expand NSBRI efforts to reach students and families.     

中英色彩语言的诠释

本文运用比较的方法分析了中英两种语言中颜色词的异同，说明由于受历史传统、社会习俗，宗教信仰以及民族心理等因素的影响，不同的民族国家表示颜色的方法和用词不尽相同。了解并掌握这些颜色词及其受文化影响而形成的各种固定用法，对中西文化交流有一定实际意义。     

先进的液氧涡轮泵的设计与开发

先进的液氧(简称ALO)涡轮泵,用于推力为222.4kN的上面级膨胀循环发动机,它的结构尺寸和性能特征是由Pratt-Whitney公司制定的,以支持整体高收益的火箭推进技术项目(简称IHPRPT)。ALO涡轮泵是由俄罗斯的Voronezh化学自动化设计局(简称CADB)设计的,该设计局是Pratt-Whitney公司的合作伙伴。ALO涡轮泵是一种为上面级液体火箭发动机设计的高性能、低成本、高可靠性的涡轮装置,所提供液氧的流量为99Ib/s(45kg/s),压力为1800psi(121bar)。该涡轮泵与泵前的增压泵一起联合使用。按预先设想,ALO涡轮泵先进之处不仅包括高可靠性和低制造成本,而且其设计和开发费用也被压缩至最低限度。设计、制造和零件的标准测试是在一个较短的周期内(大约1.5年)完成的,花费了少量的元器件和原材料。这可能部分归功于CADB对以前相似涡轮泵充分的研究。     

瑞典的探空火箭综述

介绍了瑞典航天公司发射的云雀，黑雁和ＭＡＸＵＳ探空火箭及其所用的固体火箭发动机的性能，简要讨论了瑞典探空火箭发展特点。     

图像边缘信号能量与MTF的相关研究

文章从边缘的角度出发，分析红外遥感图像质量的评价参数——边缘信号能量与调制传递函数MTF（Modulation Transfer Function）的关系。实验结果表明边缘信号能量能很好地反映MTF的变化，并针对某一特定地物建立实验室条件下边缘信号能量与MTF的数学关系模型。     

Forecasting of the Total Electron Content at a Single Location

The autocovariance prediction method previously used for the forecast of VI derived ionospheric characteristics has been used for forecast of one of the most important ionospheric—the total electron content (TEC)—at single locations. Quiet and disturbed conditions at different European stations were studied in regard to clarify the forecasting capabilities of the method for determination of the TEC. The accuracies of the method achieved in dependence on the time range of the forecast are demonstrated.     

振动温度的激波管测定

根据双原子分光带系及其强度理论,介绍了测定振动温度的原理及方法。同时,利用激波加热试验气体的方法,得到氧化铝分子绿带系(B~2∑~+-X~2∑~+)的全部光带。通过氧化铝分子绿带系光带强度的测定,得到在激波马赫数为10时,反射激波后气体的振动温度约为5200K。     

4F富里叶变换透镜系统的三维变换特性

本文从理论和实验上应用4F富里叶变换透镜系统,把三维物场转换为三维象场。象的空间位置和光场振幅的变化与透镜系统的焦距以及物体距焦平面的位置有关。根据4F系统的三维变换特性,本文还讨论了该系统对三维粒子场全息记录、再现的影响。